In two exploratory analyses with short (median 3.5 years) and longer (median 7.0 years) follow-up of women with operable breast cancer treated with adjuvant surgical oophorectomy, the proposers found that benefit from adjuvant therapy was significantly greater in women undergoing simultaneous mastectomy and oophorectomy in the history-estimated luteal phases of their menstrual cycles. The investigators have been conducting a randomized, controlled trial to investigate the hypothesis that luteal phase oophorectomy is superior to follicular phase surgery in Filipino, Vietnamese or Moroccan premenopausal women with regular menstrual cycles and hormone receptor-positive tumors, undergoing adjuvant surgical oophorectomy followed by tamoxifen therapy. Blood samples for hormonal assays are taken on the day of oophorectomy for later analysis. As of June 1, 2008, 548 women have been enrolled in the trial. Based on recent experience, the accrual goal of 762 will be reached by June 2009. Compliance with randomized assignments for dates of surgery has been good and less than 1% of cases have been lost to follow-up. With follow-up of 3.5 years from the time of last study case entry, (to December 31, 2012), the study is expected to have at least 80% power to detect a hazard ratio for disease-free survival of 0.65 comparing mid-luteal phase scheduled and immediate ophorectomy/mastectomy surgery. Four years of support is requested to complete this novel hypothesis-testing trial. PUBLIC HEALTH RELEVANCE: The goal of the study is to prove that we can improve the survival of the average (middle) woman in the trial by a year with luteal phase oophorectomy. 548 women have entered the study so far. We will also study other aspects of these treatments including how long they work in controlling the disease, and the relationships of progesterone and other hormone levels on the day of oophorectomy surgery to disease free survival. If the improvement in treatment tested works, this will have major implications for treatment of breast cancer and other solid tumors generally.